Electrically controlled printing machine employing reciprocable type bias

ABSTRACT

This device prints numbers or other characters on paper or other such material in response to digital electrical input signals. It uses linear type bars which are moved back and forth via a motor and springs, and are individually stopped at the correct characters by electrical or electromagnetic stop elements. These stops or latches are actuated via electrical comparators, which compare the electrical input signal for each type bar, typically in binary-coded-decimal code, with the electrical output of a position sensor, and stop each type bar at the proper position. Only one position sensor is needed for a plurality of type bars. A cam mechanism, in conjunction with springs, moves and raises and lowers the type bars. The type is first inked, and then the bars a re moved forward and pressed onto the paper tape or other such material. T HIS PRINTER IS PARTICULARLY SUITED FOR CONNECTION TO DIGITAL ELECTRICAL INDICATING INSTRUMENTS, SUCH AS DIGITAL VOLTMETERS. It is substantially simpler and cheaper to manufacture than other printers in this category.

United States Patent [72] Inventor John O. Yeiser Santa Ana, Calif. [21]Appl. No. 863,930 [22] Filed Oct. 6, 1969 [45] Patented Feb. 23, 1971[73] Assignees Yeiser Laboratories Inc., Costa Mesa,

Calif., Enaed Electronics, Inc., Half Moon Bay, Calif., and DeaneElectronics, Newport Beach, Calif., a fractional part nterest to e [54]ELECTRICALLY CONTROLLED PRINTING MACHINE EMPLOYING RECIPROCABLE TYPEBIAS 10 Claims, 7 Drawing Figs.

[52] U.S. (I 101/93 [51] Int. Cl B41j 1/08, 7 B4 1 j 5/30 [50] FieldofSearch 101/93, 109, 46, 94, 97, 98, 96, 202; 197/50, 51, 1

[56] References Cited UNITED STATES PATENTS 1,333,890 3/1920 Wright101/93 1,768,526 6/1930 Lasker 101/93 1,863,098 6/1932 Borel 101/931,997,167 4/1935 Bryce 101/93 Primary ExaminerWilliarn B. PennAttorneyLawrence Fleming ABSTRACT: This device prints numbers or othercharacters on paper or other such material in response to digitalelectri' cal input signals. It uses linear type bars which are movedback and forth via a motor and springs, and are individually stopped atthe correct characters by electrical or electromagnetic stop elements.These stops or latches are actuated via electrical comparators, whichcompare the electrical input signal for each type bar, typically inbinary-coded-decimal code, with the electrical output of a positionsensor, and stop each type bar at the proper position. Only one positionsensor is needed for a plurality of type bars. A cam mechanism, inconjunction with springs, moves and raises and lowers the type bars. Thetype is first inked, and then the bars a re moved forward and pressedonto the paper tape or other such material. This printer is particularlysuited for connection to digital electrical indicating instruments, suchas digital voltmeters. It is substantially simpler and cheaper tomanufacture than other printers in this category.

PATENTEU FEB23 ISYI- SHEET 1 BF 3 Imam roe ELECTRICALLY CONTROLLEDPRINTING MACHINE EMPLOYING RECIPROCABLE TYPE BIAS BACKGROUND OF THEINVENTION This invention relates to printing machines which printnumbers or other characters on paper tape or the like, in response todigital electrical signals applied to input terminals. A majorapplication of the invention is in electrical attachment to digitalelectrical measuring instruments, such as digital voltmeters, to printout the data which these instruments indicate to the eye. A purpose ofthe invention is to provide such a printer that is cheap and simple ofmanufacture, compared to the relatively complex printers of the priorart.

Printers of the category in which this invention fits are are of thefollowing general nature: One or more movable typecarrying elements,such as type bars or type wheels, are provided, with means to sensetheir positions. During the print portion of the operating cycle, theseelements are moved in a quasi-continuous manner via a motor, clutches,springs, or other suitable mechanical elements. When each of theseelements arrives at the correct position to print the characterdetermined by the electrical input signal, it is stopped and locked orlatched into position. When all these elements are so locked, they arepressed against the paper, as a group, to print the input information.

In such printers, when the characters are arabic numerals, theelectrical input signals are commonly in parallel binarycoded-decimalform, using either the well-known l2-2-4 or the l-2-4-8 codes. For eachtype-carrying element there will be, in this common case, four inputterminals (plus a common terminal).

These terminals are connected to comparators or coincidence detectors.Also, position sensors, such as decoding commutators, are provided tosense the position of each typecarrying element, and the outputs ofthese position sensors go also to the comparators or coincidencedetectors. When the position of a type-carrying element corresponds toits digital electrical input signal, the comparator or coincidencedetector will produce an output. This detector output is arranged toenergize a stop or locking device, to latch the type-carrying element inthe correct position. In this art, the position sensors may be eithermechanical or electrical.

SUMMARY OF THE INVENTION The printer of this invention employs typebars, each having a row of type, usually the arabic numerals 9 plus aspace and some punctuation, near one end. Several identical bars, suchas 4 to bars, are typically used. The whole group of bars is swept ordrawn back simultaneously, away from the paper roller, by a yoke-and-pinmechanism. Then the bars are permitted to move forward, each urged alongby an individual spring. Each bar is stopped and locked at the correctposition by an individual electromagnetic latch mechanism. When all thetype bars are latched, the whole group of bars is pressed against thepaper by a cam mechanism.

The latches are energized by electronic converter and comparatorcircuits. In these circuits, the parallel binary-codeddecimal (BCD)input signal corresponding to each type bar may be converted to ananalogue voltage. This voltage may then be compared electrically with asecond analogue voltage which represents the position of the type bar.This second analogue voltage may be derived from a single positionsensor (such as an ordinary potentiometer) which is linked mechanicallyto the yoke mechanism, common to all the type bars. This is considered acheap, novel, and reliable way to sense the positions of all the bars insuccession. Its operation will be described in detail below.

In the remainder of the mechanical structure, a motor drives a camwheel. Links from this wheel move the yoke, and also advance the paper.A cam follower on the cam raises and lowers the type bars twice in eachoperating cycle. They are raised during the times that they must moveback and forth, and are lowered twice during a cycle: once for inking,and again for pressing against the paper.

SHORT DESCRIPTION OF DRAWINGS FIG. 1 is a semidiagrammatic, partiallycutaway, perspective view of the essential parts of the mechanism of theinvention;

FIGS. 2, 3, 4, and 5 are side views of the major mechanical parts of theinvention in connection with one type bar, showing four stages in itsoperating cycle, to illustrate its operation;

FIG. 6 is a block schematic diagram of the main portions of theelectronic circuitry used in conjunction with the mechanisms of theinvention; and

FIG. 7 is a schematic diagram of the electronic circuitry which may beused in conjunction with one of the type bars in the mechanism of theinvention.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows the mechanicalworking parts of the invention in a semidiagrammatic, partially cutawayview, and will be described first. This is a preferred form of theinvention, but is not considered limiting. In FIG. 1, the frame isomitted for clarity. Parts which are attached to the frame of themachine are indicated by ground symbol hatching, as at the variouspoints designated 20 in FIG. 1.

A complete type bar is shown at 1. Two more identical such bars 1, 1",are shown partially. More such bars may obviously be used, such as 4 or6 or 10 of them.

These type bars may rest on a bar or guide 2, across which they all mayslide. At the forward portion of a type bar such as 1, a row of type maybe attached, as at 3 in FIG. 1, representing for example the arabicnumerals O to 9, plus suitable punctuation marks and a space. This typemay make marks on paper or other suitable film material 4, passingaround a roller 7 12, and coming from a supply roll 6. To ink the type,an ink pad 7 is shown, against which the type 3 may be pressed before itis moved forward and pressed downon the paper 4. With various knownvarieties of ink, such as fluid stamp pad ink, no difficulties areexperienced with ink buildup on the type faces.

The type bars 1, etc., have long slots 13 and 14. A pin 19 passesthrough all the slots 13. The ends of the pin 19 fit into the slottedends 15, 15 of the yoke 16. Yoke 16 can rock back and forth on shafts17. On moving back (toward the left in FIG. 1), it can collect all thetype bars, via pin 19, and sweep or draw them to their rearmostposition.

Yoke 16 is moved back and forth by a crank arm 39 which is driven frompoint 18 on a cam wheel 5. This cam wheel 5 is driven in rotation by amotor 21 (which motor is located inside the machine in practice, but isdrawn here in an outboard location for clarity). When a print command isgiven the motor 21 turns cam wheel 5 through one revolution, then stops.The control apparatus that does this is conventional, and will bedescribed later.

Also driven from point 18 on cam wheel 5 is a lever 23, via a crank arm22, which advances the paper. This advancing is done by means of anoverrunning clutch 24 which connects lever 23 to shaft 25; and shaft 25turns the paper roller 12. The overrunning clutch 24 is illustrated asbeing of the coil spring type, but may be of any convenient knownvariety, such as a pawl and ratchet.

Thus, when motor 21 turns the cam wheel 5, crank arms driven therefromat point 18 will rock the yoke 15 back and forth, and will also advancethe paper via lever 23.

The cam wheel 5 has two identical depressed portions 26, located apart.These operate to raise and lower the triangle-shaped cam follower 27.The stationary pivot point of this cam follower is at shaft 28. Theupper corner of the cam follower 27 carries a pin 29, which passesthrough the forward slots 14 of all the type bars 1, 1', 1", etc. Thepurpose of this pin 29 is to raise and lower the forward(type-carrying).ends of the type bars. When the comer 30 of cam 27 isdown in a depressed portion or notch 26 of cam 5, the pin 29 pulls thetype bars down. At one part of the operating cycle, it pulls them downagainst the ink pad 7. At another part of the cycle, it pulls them downagainst the paper 4 on roller 12, to print.

In between these events, the corner portion 30 of cam 27 rides uponhigher portions of cam 5 and the type bars are accordingly raised up outof possible contact with either ink pad 7 or paper 4. In practice, theamount of vertical motion is small, of the order of 0.01 to 0.05 inch.While the type bars are thus raised up, their longitudinal motion,produced by yoke 16 or springs 31, takes place.

This brief discussion of the operating cycle of the printer of theinvention is intended only to clarify the description of the structure.The operating cycle is described in detail in a later section of thisspecification, in connection with FIGS. 2-5.

Springs 31, 31', 31", etc. are provided to move the type bars 1, 1', 1",etc. forward individually during the appropriate portion of theoperating cycle. The forward (right-hand, in FIG. 1) ends of thesesprings are anchored to an appropriate stationary point on the machineframe. as indicated at 20.

Each type bar 1, 1', 1", etc. has a row of notches or teeth 32 alongpart of its length. These are spaced the same distance apart as the typecharacters in row 3. Disposed so as to engage with these notches orteeth 32 are latching elements 33. There is one for each type bar. Whenattracted by electromagnets 34, 34', etc., these latching elements willmove so as to engage the notches or detents 32, and so lock the type barwith a selected type character opposite medium support or roller 12, inposition to print said character on paper or medium 4. This is evidentfrom FIGS. 1 and 3.

The motor 21, FIG. 1, is controlled in a conventional way. A cam 35,turning with cam wheel 5, engages a contact spring 36 once in eachrevolution, and separates this contact 36 from a stationary contact 37,opening the motor circuit. To start the operating cycle, a switch 38 isclosed momentarily; and the motor 21 turns through one revolution andthen stops itself by separating contacts 36, 37 via the cam 35.

The positions of type bars 1, 1', 1", etc. may be sensed successively bymeans of a position sensor or transducer 41, FIG. 1, which may be forexample an ordinary potentiometer, a differential transformer, or otherknown means. This sensor may be connected mechanically to sense thepositions of the type bars through a link or rod 40 connected to yoke16, whose position will at some time correspond to all the possiblepositions of all the type bars. Trigonometric errors may be corrected inany of the known ways, such as suitably tapering the curve of resistanceratio vs. position of the transducer 41, or by driving it by other knownmeans, such as by pulleys and dial cable. It is noted that the accuracyrequired of sensor 41 is no more than a few percent of full scale. Otherwell-known position sensing means may be used, such as decodingcommutators.

Sensor 41 in FIG. 1 is semidiagrammatically illustrated as a linearpotentiometer of the type common in the art of electronicinstrumentation. It may comprise a case (41), an operating rod orplunger 124, a linear resistance element 121, and a sliding contact orslider 122 making movable contact with resistance element 121. Slider122 is mechanically connected internally of the case to the plunger 124,as indicated by dotted line 125, so that when plunger 124 is pushed in,slider 122 moves toward the left-hand end of resistance element 121; andwhen pulled out, it moves the point of contact toward the right-hand endof element 121. With a battery or other suitable source of voltage 123connected in the conventional maniter as shown, the output voltage e, ofthis potentiometer or sensor will increase as plunger 124 is pulled out,and decrease as it is pushed in. For a given voltage of source 132, theoutput voltage e, will have a different, known, value corresponding toevery position of plunger 124. A voltage or signal such as e,, in thisspecification is termed a position signal. In the circuitry of FIG. 7,the sensor 41 is shown connected similarly, except that the voltagesource, instead of source 123, is the common power supply 61. It isobvious that any suitable type of displacement transducer or positiontransducer known to the art of instrumentation could be used in place ofa linear potentiometer at 41. Such as a linear variable differentialtransformer (LVDT) with appropriate circuitry;

or a rotary potentiometer or the like driven through a mechanical rackand pinion or a flexible cable or the like.

The exact function of the single transducer or sensor 41, in cooperationwith the latching elements 33, 34, and with the control circuitry yet tobe described (FIGS. 6 and 7) will be given in a later section inconnection with FIGS. 2-7 of the drawing.

MODE OF OPERATION OF THE INVENTION FIGS. 2, 3, 4, and 5 illustratemechanically the four majo: stages in the operating cycle of the printerof the invention, in connection with one type bar 1 (for clarity). InFIG. 2, the cam wheel 5, revolving counterclockwise as indicated byarrow 40, has moved yoke 16 all the way back (to the left). Yoke 16 hasswept or drawn type bar 1 all the way back, through pin 19 riding inslot 13. At this same time, cam follower 27 has gone down into a lowspot or notch 26 in cam 5, moving the forward end of type bar 1 (via pin29 in slot 14) down against the ink pad 7, to ink the type. Positionsensor 41 is at its rearmost position.

FIG. 3 shows a second part of the operating cycle, mechanically. Here,the yoke 16 has moved forward (to the right) to the position where thetype bar 1 is locked into position. The propulsive force to move typebar 1 forward is furnished entirely by spring 31; the yoke 16, ineffect, holds it back. At this point, the electromagnet 34 has beenenergized in response to a signal from the comparator or coincidencedetector (described later), and has moved the latch element or armature33 so that it latches into one of the notches or teeth 32 on type bar 1.

As is known in the art, a comparator circuit receives two electricalinput signals and produces an electrical output signal when the twoinputs are substantially equal. This is explained fully in connectionwith FIGS. 6 and 7. In connection with FIG. 3, it is sufficient to notethat one input signal to a comparator such as 62 (FIGS. 6-7 is derivedfrom an external input signal representing the selected character to beprinted, and the other from position sensor 41. When the plunger 124 ofsensor 41 is in such a position that the selected character on a typerow 3 is in line with paper roller or medium support 12, the twocomparator inputs will agree; and the comparator will produce anelectrical output, here termed a latching signal. This will act tooperate the appropriate latching device 34, etc, to latch the type barin place to print the selected character.

Type bar 1, at this point, has also been raised up, off the ink pad, bycam follower 27, so that is has been free to move longitudinally. Thevertical motion is exaggerated for clarity of illustration; in practiceit is typically of the order of 0.0l to 0.05 inch.

FIG. 4 shows the mechanical situation at a further stage in the cycle,where the bar, now latched into position at the correct character, ispressed down against the paper. The corner of the cam 27 has gone downinto a notch or low spot 26 of the cam 5, and so lowered the selectedtype bar 1 so that one of the characters in row of type 3 (which row hasbeen inked) is pressed against the paper 4, making a printout. Ofparticular significance is the fact that the latch 33 has stopped thetype bar from moving (when it was urged forward by spring 31)- but thatthe pin 19, moved by yoke 16, continues forward as if nothing hadhappened. This is the purpose of the slot 13.

FIG. 5 shows the mechanism near the end of the operating cycle, where itis nearly back to the situation of FIG. 2. Cam 5 has raised follower 27up, so that type 3 is up off of the paper 4. Arm 39, connected to earnwheel 5, is moving type bar 1 backward, against the pull of spring 31(note that pin 19 is, necessarily, now against the back end of the slot13). Electrornagnet 34 has released the latch or armature 33, so thattype bar 1 has been free to move longitudinally. The next stage will belike FIG. 2 again, where arm 39 has moved yoke 16 all the way to theback, and cam 5 has lowered the type bar, via cam follower 27, back downonto the ink pad 7.

It is to be noted that, wherever a latching device 34, 33 may stop atype bar during the forward portion of the cycle (FIGS. 3, 4), the pin19 can continue to move freely to the end of its travel. The yoke 16,through pin 19, operates to draw or sweep the type bars back, but itdoes not force them forward. Instead, the pin 19 slides in the slots 13.The type bars are stopped by their individual latching devices 34, 33,in response to outputs from the control circuitry.

FIGS. 6 and 7 show the comparison and control circuitry. FIG. 6 is ablock diagram of the circuitry for three type bars. More bars mayobviously be used, with appropriate duplication of the circuitry blocks.In FIG. 6, three comparator circuit blocks 62, 62, 62" are shown. Eachhas an output that energizes an individual magnetic latching device 34,33, etc., to latch one type bar into the correct position. The circuitblocks are fed the necessary DC power from a common supply 61. Sets ofinput terminals 63, 63, 63", etc., are provided for each of the circuitblocks. BCD or other types of parallel binary digital input signals,from external sources, are applied to these terminals. A position inputsignal from position sensor 41 (a function of the displacement orposition of plunger 124) is fed commonly into position-input terminals64, 64, 64", etc., of all the circuit blocks 62, etc., at once.

In this system, FIG. 6, which uses only one position sensor 41, theoperation of the circuit blocks may be explained by the followingexample: Assume that the coded digital signal at input 01 represents thearabic numeral 1, that the signal at input 02 represents numeral 9, andthat the signal at input 03 represents numeral 4. Referring briefly backto FIGS. 2 and 3, the type bars (in this case, three of them) will moveforward. When the output of position sensor 41 reaches a valuecorresponding to numeral 1, this fact will be recognized by whichever ofthe comparator circuits has a coded 1 applied to its input. Thatcomparator will, through the associated energizing circuit, energize itscorresponding latch. In this case, it will be comparator 62, FIG. 6.Those comparators whose inputs correspond to larger numbers are not yetready to function; a 1 output from the position sensor 41 is of noimmediate interest to a comparator that has, say a 4 input.

As the two remaining type bars continue to move forward, position sensor41 gets to the point where it is delivering a 4 output. This matchesinput 03, to comparator 62" which immediately energizes latch 33" andstops that type bar at 4; The one remaining type bar continues forwarduntil the sensor output matches the 9 signal at input 02. Then, thecomparator 62' energizes latch 33 and stops that bar at 9.

Referring to FIG. 4, all three type bars are now latched in theircorrect respective positions, and the cam follower 27 presses the typeagainst the paper 4, and prints 194. It is noted that in this system thetype bars are latched in the order of the magnitude of the charactersthat they are to print, all during a single cycle of operation.

COMPARATOR CIRCUITRY FIG. 7 is a schematic diagram of a preferred formof the circuitry which may be used in each of the blocks 62, 62, etc. ofFIG. 6. Shown also in FIG. 7 are position sensor 41 and anelectromagnetic latch 34, 33.

In FIG. 7, input tenninals 70, 71, 72, 74, 78 are provided for theexternal input signal. In this example, the signal may be in the 1-2-4-8BCD code. Conventional current-limiting and return resistors 101 may beassociated with each input terminal (except common terminal 70). Inputterminal 71 is connected, through such a resistor, to the controlterminal of an active circuit device 81, in this case a transistor(although SCRs and other kinds of electronic switching devices may beused, or even relays). The signal voltage applied to terminal 71 isassumed to be large enough, e.g., 1 or a few volts, to make device 81switch on, as by saturating it if it is a transistor. Input terminal 72goes similarly to a like device 82; terminals 74 and 78 to like devices84 and 88.

Each of these active devices has a load resistor 91, 92, 94, 98,connected to a common point 99. The values of these resistors are choseninversely to the relative magnitudes that they represent, i.e., 1, 2, 4,or 8. Point 99 is maintained at a substantially constant DC voltage withrespect to common terminal 70, as by being connected to the emitter of atransistor 110, whose base is connected to the tap on a voltage divider68, 69 across power supply 61. Load resistor 91 may for exam ple bechosen so that when device 81 is saturated on "on," I milliampere flowsthrough it. Similarly, load resistor 92 may be chosen to pass 2milliamperes when its switch device 92 is on; and load resistors 94 and98, to pass 4 and 8 milliamperes respectively. Only the resistanceratios matter; their absolute magnitudes are of minor importance. Itwill be seen that the circuitry so far described constitutes aBCD-to-analogue current converter. Thus, a BCD 5 input would constituteapplying switching voltage to input terminals 71 and 74; and the currentat summing point 99 would be an analogous 5 milliamperes.

The analogue current at point 99 is now converted into a proportionatevoltage by means of active element 110, typically a transistor. Sinceits collector current is nearly equal to its base current-the current atpoint 99the voltage drop across its collector load resistor 111 will beanalogous. From. the input terminals 71, etc., to the load resistor 111,the circuit is a BCD-to-analogue voltage converter.

The comparator circuitry including devices 112, 113 compares theanalogue voltage drop across resistor 111 with the output of positiontransducer 41, and energizes the latch 34 when one exceeds the other.The analogue of the signal input e is applied to a control ten'ninal ofactive device 112, at point 118. The position sensor output e, isapplied to a similar device 113, at point 119. Both devices may betransistors in the long-tailed pair type of circuit, with a commonemitter load 114. The output of device 112 is coupled to an energizingcircuit using a power transistor or other suitable switching devicethrough conventional coupling resistors 115, 116. This electrical outputat point 119 may be termed a latching signal. When the voltage e becomesless than the voltage e,, device 112 will conduct, and switch the powerdevice 117 on, which will then energize the latch magnet 34 and stop thetype bar.

It is not usually necessary to use a regulated power supply at 61,because the effect of supply variations on voltages e and e is similar.

After that part of the operating cycle where the printing takes place(FIG. 4), the yoke 16 moves back, and drives the plunger 124 of positionsensor 41 back. During this return stroke, the sensor output will passback through all the values that it had when the comparators 112, 113(FIG. 7), and the energizing circuit, energized the latching magnets 34,etc. As it does so, each of the comparators will cause its associatedpower device such as 117, to cease conducting and release thecorresponding latch magnet 34, etc. Thus, when the type bars are sweptall the way back, all the latches 34, etc. have been released, and theprinter is ready for another cycle.

I claim:.

1. A printing machine comprising:

a plurality of bars each carrying a row of type and adapted to print acharacter selectively on a medium, a medium support;

each said bar being movable longitudinally between a starting positionand a printing range of positions generally opposite said mediumsupport;

sweep means to draw said bars collectively to said starting position;

spring means to draw said bars individually into said printing range;

latching means to latch each said bar at a selected position in saidprinting range with a selected character opposite said medium support;

press means to press said bars against said medium support to print saidselected characters on said medium;

sensing means translating the longitudinal position of each said barinto an electrical position signal;

a set of input terminals for each said bar to receive input signalsrepresenting said characters selectively;

comparators connected to receive functions of both said input andposition signals and each producing a latching signal when they agree;

energizing means operating said latching means in response to saidlatching signal; and

whereby said input signals select each of said selected characters to beprinted by said press means.

2. A printing machine as in claim 1, further comprising:

an ink pad;

means synchronizing said press means with said sweep means; and

said press means pressing each said row of type onto said ink pad whensaid bars are substantially in said starting position, and holding saidbars out of contact with said pad between said starting position andsaid range of printing positions.

3. A printing machine as in claim 1, further comprising:

an inking element;

driving motor means;

said sweep means comprising a swingable yoke and a reciprocating linkageconnecting said yoke to said motor means, said yoke engaging a first pinwhich passes through first longitudinal slots in said bars; and

said press means comprising an oscillatory mechanism connected to saidmotor means and to said bars, and adapted to press said type alternatelyagainst said inking element and said medium.

4. A printing machine as in claim 3, wherein:

said oscillatory mechanism comprises a cam, a cam follower, and a secondpin;

said second pin passing through second longitudinal slots in said barsto impart motion to them substantially normal to their length.

5. A printing machine as in claim 1, further comprising:

driving motor means connected to rotate a crank pin;

a first cam, and a second cam;

longitudinal slots in said bars, and slot pins passing slidably throughsaid slots;

said sweep means comprising a swingable pivoted yoke and a connectingrod connecting it to said crank pin; said yoke engaging one of said slotpins;

said press means comprising a follower on said first cam connected tothe other of said slot pins;

said second cam engaging electrical contacts connected to stop saidmotor means when said machine is substantially in said startingposition; and

manual switch means connected to said contacts to start said motor meansto initiate an operating cycle.

6. A printing machine as in claim 5, wherein:

said medium support is a roller supported in printing relation to saidrows of type, and further comprises:

an overrunning clutch connected to rotate said roller, and a cranklinkage between said clutch and said motor means; and

said linkage and clutch rotating said roller through a predeterminedangle for each revolution of said crank pm.

7. A printing machine as in claim 1, wherein:

said sensing means comprises a single mechanoelectric displacementtransducer, and a driving linkage connecting the mechanical operatingelement of said transducer to said sweep means:

8. A printing machine as in claim 1, further comprising:

an electronic digital-to-analogue converter connected between said inputterminals and each said comparator and producing an analogue voltagefunction of each said input signal;

said sensing means comprising an electrical analogue displacementtransducer producing an analogue position si al; and

sai comparator being connected to receive said analogue voltage functionand said analogue position signal.

9. A printing machine as in claim 8, wherein:

each said converter comprises four electrical switching elements, eachconnected to a load resistor of weighted value;

all said load resistors being connected to a current-summing junction;

an electrical translating device connected to translate the sum of saidcurrents into an analogous voltage; and

said voltage constituting said analogue voltage function.

10. A printing machine as in claim 9, wherein:

said switching elements and said translating device are transistors;

said comparator comprises two transistors in a commonemitterdifferential connection; and

said energizing means comprises a power transistor connected to receivea latching signal from a point in the collector circuit of saidcomparator.

1. A printing machine comprising: a plurality of bars each carrying arow of type and adapted to print a character selectively on a medium, amedium support; each said bar being movable longitudinally between astarting position and a printing range of positions generally oppositesaid medium support; sweep means to draw said bars collectively to saidstarting position; spring means to draw said bars individually into saidprinting range; latching means to latch each said bar at a selectedposition in said printing range with a selected character opposite saidmedium support; press means to press said bars against said mediumsupport to print said selected characters on said medium; sensing meanstranslating the longitudinal position of each said bar into anelectrical position signal; a set of input terminals for each said barto receive input signals representing said characters selectively;comparators connected to receive functions of both said input andposition signals and each producing a latching signal when they agree;energizing means operating said latching means in response to saidlatching signal; and whereby said input signals select each of saidselected characters to be printed by said press means.
 2. A printingmachine as in claim 1, further comprising: an ink pad; meanssynchronizing said press means with said sweep means; and said pressmeans pressing each said row of type onto said ink pad when said barsare substantially in said starting positioN, and holding said bars outof contact with said pad between said starting position and said rangeof printing positions.
 3. A printing machine as in claim 1, furthercomprising: an inking element; driving motor means; said sweep meanscomprising a swingable yoke and a reciprocating linkage connecting saidyoke to said motor means, said yoke engaging a first pin which passesthrough first longitudinal slots in said bars; and said press meanscomprising an oscillatory mechanism connected to said motor means and tosaid bars, and adapted to press said type alternately against saidinking element and said medium.
 4. A printing machine as in claim 3,wherein: said oscillatory mechanism comprises a cam, a cam follower, anda second pin; said second pin passing through second longitudinal slotsin said bars to impart motion to them substantially normal to theirlength.
 5. A printing machine as in claim 1, further comprising: drivingmotor means connected to rotate a crank pin; a first cam, and a secondcam; longitudinal slots in said bars, and slot pins passing slidablythrough said slots; said sweep means comprising a swingable pivoted yokeand a connecting rod connecting it to said crank pin; said yoke engagingone of said slot pins; said press means comprising a follower on saidfirst cam connected to the other of said slot pins; said second camengaging electrical contacts connected to stop said motor means whensaid machine is substantially in said starting position; and manualswitch means connected to said contacts to start said motor means toinitiate an operating cycle.
 6. A printing machine as in claim 5,wherein: said medium support is a roller supported in printing relationto said rows of type, and further comprises: an overrunning clutchconnected to rotate said roller, and a crank linkage between said clutchand said motor means; and said linkage and clutch rotating said rollerthrough a predetermined angle for each revolution of said crank pin. 7.A printing machine as in claim 1, wherein: said sensing means comprisesa single mechanoelectric displacement transducer, and a driving linkageconnecting the mechanical operating element of said transducer to saidsweep means.
 8. A printing machine as in claim 1, further comprising: anelectronic digital-to-analogue converter connected between said inputterminals and each said comparator and producing an analogue voltagefunction of each said input signal; said sensing means comprising anelectrical analogue displacement transducer producing an analogueposition signal; and said comparator being connected to receive saidanalogue voltage function and said analogue position signal.
 9. Aprinting machine as in claim 8, wherein: each said converter comprisesfour electrical switching elements, each connected to a load resistor ofweighted value; all said load resistors being connected to acurrent-summing junction; an electrical translating device connected totranslate the sum of said currents into an analogous voltage; and saidvoltage constituting said analogue voltage function.
 10. A printingmachine as in claim 9, wherein: said switching elements and saidtranslating device are transistors; said comparator comprises twotransistors in a common-emitter differential connection; and saidenergizing means comprises a power transistor connected to receive alatching signal from a point in the collector circuit of saidcomparator.